Conventionally, when two circuit boards are connected together electrically and mechanically, one circuit board is connected to a male connector having a plug contact, and the other circuit board is connected to a female connector having a socket contact. Then, the male and female connectors are connected to each other.
When housed in an electronic device, the circuit boards thus connected together are subjected to expansion and contraction and hence warpage due to changes in the environmental temperature of the electronic device. If the electronic device is impacted by being dropped or other causes, the circuit boards are subjected to an impact force and hence bending. Such warpage and an impact force cause stress at the junctions between the circuit boards and the connectors. In the case of the aforementioned pair of male and female connectors, the stress is absorbed by the stiffness of the socket contact, which is made of an elastic thin metal sheet.
Such a connection using male and female connectors, however, is high cost because especially the female connector has a complicated structure. In addition, these connectors occupy a large space, so that such a connection is difficult to be applied to an electronic device required to be smaller and thinner.
As another method for connecting circuit boards together, connectors having contact pins are directly connected to circuit boards, which are placed on the top and bottom surfaces of an insulating resin frame. This connection method is also required to reduce stress at the junctions between the circuit boards and the contact pins.
An example of such a connection method to reduce stress is shown in Japanese Patent Unexamined Publication No. S62-37887 which discloses a connector of FIGS. 17 to 19 as a substrate connecting member. FIGS. 17 and 18 are the front view and the plan view of the connector, respectively. FIG. 19 is a sectional view showing a state where a contact pin of the connector is directly soldered to a circuit board.
Connector 92 includes frame 93 having a plurality of contact pins 94 inserted therein. Frame 93 has slit grooves 95, which are formed alternately from both side walls of frame 93 in such a manner as to extend beyond the position of contact pins 94 and to be positioned between contact pins 94. When the electronic device using connector 92 has a temperature change, this may cause the difference in the coefficient of thermal expansion between circuit board 91 and frame 93 and hence stress at soldered portion 96. However, according to the disclosure, slit grooves 95 function to reduce the stress.
In FIG. 19, contact pin 94 projecting from frame 93 is directly connected at its upper portion to another circuit board, which is not illustrated.
In the structure where a frame having contact pins inserted thereinto is provided with slit grooves as described above, the stress caused by the expansion and contraction of circuit boards can be reduced. In the case where the connecting structure of the circuit boards is used in an electronic device and the circuit boards are warped due to temperature changes in the electronic device or bent due to an impact load generated when the electronic device is dropped, stress is applied to the junctions between the circuit boards and the contact pins. The aforementioned structure, however, cannot sufficiently reduce the stress applied to the junctions.
Furthermore, as electronic devices are getting smaller and denser, circuit boards having electronic components mounted thereon are increasingly required to be connected together in a large area. For this reason, circuit boards are required to be connected together throughout their outer peripheral portions. However, in such a connection, the weight of the electronic components mounted on the circuit boards increases the impact load to be applied to the connecting members, thereby possibly damaging the reliability of the junctions.